Mesoscale Variabilities in Sea Surface Current Fields Derived Through Multi-Sensor Tracking of Sea Surface Films
Seppke, Benjamin; Gade, Martin; Dreschler-Fischer, Leonie
University of Hamburg, GERMANY
The investigation of mesoscale turbulent sea surface currents is of high interdisciplinary interest, since it results in a better understanding of ocean-atmosphere interactions and may help to improve numerical model results, particularly in coastal waters. In recent studies, we have already shown that it is possible to derive mesoscale sea surface current fields by tracking signatures of marine surface films in multi-sensor satellite data. Although the derived sea surface current fields corresponded well with those provided by numerical models, the former mainly showed large-scale current properties. This is insofar remarkable, as the traced signatures clearly follow local dynamical features such as eddies or dipoles.
In this paper, we present a new approach, which allows to extract, and even over-emphasize, the affine local current component for the derived current fields. Depending on the spatial resolution of the derived current fields this method allows a deeper insight into the turbulent nature of those fields. First results of the application of our method will be presented for sea surface currents, which have been derived using SAR- and multispectral imagery of the Baltic Sea and the Southern California Bight. In contrast to the mostly large-scale ('global') currents, the results demonstrate that there is a strong correspondence between the eddy-like signatures and the mesoscale ('local') surface current components. However, in some cases, local currents may be correlated even without corresponding image signatures. As a result, the imaged signatures can be seen as local variabilities of sea surface currents of larger scales. Moreover, these local variabilities seem to be mainly independent of the ‘global’ currents.